The present invention relates generally to a transducer and, more particularly, to a shock resistant transducer particularly suitable for hearing aids.
Transducers are particularly useful in hearing aids. The transducer may be used as a microphone to convert acoustic energy into electrical energy or as a receiver to convert electrical energy into acoustic energy. Typical transducers suitable for hearing aids comprise a coil having a first air gap, a magnetic member having a second air gap and an armature with an armature leg that extends through both of the air gaps. A diaphragm connects to the armature leg.
The operation of the transducer follows. Vibrations of the diaphragm are transmitted to the armature leg, and the vibrating armature leg causes an electric alternating electric current in the coil. Conversely, an alternating current supplied to the coil causes a vibration of the armature leg, which is transmitted to the diaphragm. Under normal conditions the vibrations of the armature leg are relatively small displacements. In extreme cases, however, the armature leg may deflect a large amount and touch the magnetic member.
One problem with the conventional transducers is that a shock or impact load exerted on the transducer may cause plastic deformation of the armature leg. For example, when the transducer falls and contacts a solid object, the armature leg deflects or bends so far that undesirable plastic deformation can occur in the armature leg. Once the armature leg is plastically deformed such that it is closer to one side of the magnetic member than the other in a steady-state condition, the transducer does not function properly.
Some conventional transducers have attempted to address this shock problem. For example, Knowles Electronics, Inc. produces a transducer (e.g. Model ED1913) with deformations on a central portion of the armature leg that is positioned within the air gap of the coil. When the Knowles transducer suffers a shock, the armature leg deflects until the deformations contact the surface of the coil, thus limiting the freedom of movement of the armature leg. One example of the Knowles transducer is generally disclosed in U.S. Pat. No. 5,647,013. Another example of a conventional transducer with shock resistance is produced by the assignee of the present applicant Microtronic BNV. The Microtronic transducer (2300 series) has a rotated coil with respect to the magnetic member. This rotation forms a stop for the armature leg to inhibit excessive bending of the armature leg in the occurrence of a shock. One example of the Microtronic transducer is generally disclosed in European Patent Application No. 847,226.
One disadvantage of the above transducers is that the shock resistance, though improved, does not meet the increasing shock standards of the hearing aid industry. Furthermore, especially for the Knowles transducer, special and/or additional parts must be used to provide the shock resistance which increase the expense of the transducer.
It is a general object of the present invention to solve the above problems. More particularly, there is desired a transducer with superior shock resistance, and which can be easily assembled from standard parts at a low cost.
According one aspect of the present invention, there is provided a transducer comprising a coil having a first air gap, a magnetic member having a second air gap and an armature. The armature includes an armature leg extending through the first air gap and the second air gap. The armature leg is capable of movement within the air gaps. The magnet member has at least one nub extending into the second air gap that limits the range of motion of the armature leg to inhibit large deflections of the armature leg and plastic deformation. The nubs may be comprised of a drop of adhesive.
In another aspect of the present invention, there is provided a transducer suitable for hearing aids comprising a coil having a first air gap, a magnetic assembly having a second air gap and an armature. The armature includes an armature leg that extends through both the first air gap and the second air gap. The armature leg is capable of movement within the second air gap. The magnetic assembly has a cushioning element secured to the magnetic assembly that extends into the second air gap. When the transducer is subjected to a shock, the movement of the armature leg is limited as it engages the cushioning element. Furthermore, the cushioning element may comprise a soft material to absorb a portion of an impact of the armature leg when the armature leg moves into contact with the cushioning element.